At the age of seven all Spartan boys were taken from their mothers and made to live in all-male groups where they were trained in the arts of war and survival.

Plutarch, writing ca 100 AD:

Lycurgus [the Spartan lawgiver] did not put Spartiate children in the care of any tutors who had been bought or hired. Neither was it permissible for each father to bring up and educate his son in the way he chose.

Instead, as soon as boys reached the age of seven, Lycurgus took charge of them all himself and distributed them into Troops [the Spartan word was "herd"]: here he accustomed them to live together and be brought up together, playing and learning as a group. The captaincy of the troop was conferred upon the boy who displayed the soundest judgement and the best fighting spirit. The others kept their eyes on him, responded to his instructions, and endured their punishments from him, so that altogether this training served as a practice in learning ready obedience. Moreover as they exercised boys were constantly watched by their elders, who were always spurring them on to fight and contend with one another: in this their chief object was to get to know each boy's character, in particular how bold he was, and how far he was likely to stand his ground in combat.

The boys learned to read and write no more than was necessary. Otherwise their whole education was aimed at developing smart obedience, perseverance under stress, and victory in battle. So as they grew older they intensified their physical training, and got into the habit of cropping their hair, going barefoot, and exercising naked. From the age of twelve they never wore a tunic, and were given only one cloak a year. Their bodies were rough, and knew nothing of baths or oiling: only on a few days in the year did they experience such delights. They slept together by Squadron and Troop on mattresses which they made up for themselves from the tips of reeds growing along the River Eurotas, broken off by hand without the help of any iron blade. During winter they added the so-called thistledown and mixed it into the mattresses, since it was a substance thought to give out warmth.

By this age the boys came to be courted by lovers from among
the respectable young men.

~Plutarch, Life of Lycurgus, 16, 17, translated by Talbert.

There were probably four categories of males within the agogé:

1. Boys aged 7 - 17, called Paides.

2. "Youths of fighting age," aged 18 - 19, called Paidiskoi.

3. Eirenes, aged 20, that is, at least two years beyond the class of boys, and who had charge of a troop or herd -- Boua -- of younger males.

4. Young Men, aged 20 - 29, called Hebontes.

At the age of 30, men married, and joined an all-male dining club or mess, the Phidition.

This is classicist W. G. Forrest's description of the agogé:

... After six years with his mother, the child who had been accepted was taken from home and enrolled in a group of his contemporaries under the leadership of an older boy ...

With his group the boy lived for the next fourteen years as he worked his way up through the increasingly brutal and brutalising training schedules which passed for education among the Spartans. Music and dancing he would learn, for both had their military uses, but reading and writing, as Plutarch remarks, 'only because they were unavoidable'. For the rest everything was designed to produce toughness, endurance and discipline ...

So schooled, at the age of twenty or thereabouts, the young man graduated to another class, that of the so-called eirenes, in which he remained for a part, perhaps even the whole of, his twenties, not yet a full citizen but liable for military service and for the time being occupied in doing to others as he had been done by, acting as leader of a younger group, ... and, a nice touch, allotted to one of two large teams to encourage rivalry in bravery, such rivalry that 'members of each team fall to fighting each other whenever they meet'.

At the age of thirty the Spartan was admitted to the assembly. Whether he had already received the other mark of manhood, admission to a sussition [an eating-club or mess], either on becoming an eiren or on ceasing to be one, is unknown ...

This was the last formal test the Spartan had to pass. Beyond it lay freedom, freedom to marry, to lead something like a normal life. His duties were light -- he had to dine with his fellows, to train with them and to fight with them; and from his kleros [land allotment] he had to provide the stipulated contribution to maintain the mess.

But it is easy to underestimate the effect even of this amount of communal living in a society where there was no other focus for a man's interests. The Spartan did not work -- he trained, with the men of his mess, he fought, with the men of his mess, or he was idle, again for the most part, one would imagine, with the men of his mess.

Many writers have commented that this sort of training, which encouraged strong -- indeed ferocious -- same-sex bonds between the warriors, was not unusual in Warrior societies.

This is from Peter Wilcox, writing about the Celts:

From early puberty the young man of the warrior caste progressed through the martial arts of the Celt, with the accompaniment of hunting, feasting, and drinking. As a fully-fledged warrior he would support and be supported in battle by a close age group of his own peers, who had been with him throughout his training for manhood. In this way many young men developed a strong man-to-man bond; and Diodorus, Strabo, and Athenaeus all remark that homo-erotic practices were common among the Celts.

As they were among the Spartans.

Classicist JE Lendon:

At Sparta lover and beloved stood beside each other in the hoplite line; before battle the Spartans sacrificed to Eros, to love.

And, Prof Lendon adds,

such relationships were institutionalized, played a large role in the training of boys, and were thought to contribute to bravery in combat.

Classicist Werner Jaeger:

It is, after all, easy to understand how a passionate admiration of noble bodies and balanced souls could spring up in a race which for countless years had prized physical prowess and spiritual harmony as the highest good attainable by man, and which had striven by grave and ceaseless rivalry, by exertion involving the utmost energies of mind and body alike, to bring those qualities to the greatest possible perfection.

Men who loved the possessors of those enviable qualities were moved by an ideal, the love for areté. Lovers who were bound by the male Eros [the God of Romantic Passion] were guarded by a deeper sense of honour from committing any base action, and were driven by a nobler impulse in attempting any honourable deed.

The Spartan state deliberately made Eros [male-male love] a factor, and an important factor, in its agogé.